Search

The diversification of cropping sequences has a positive impact on soil organic carbon, while improving nutrient cycling and crop yields. The objective of this research was to assess amylase, cellulase, C and N dynamics, and maize yield on a low fertility oxisol in the Brazilian Cerrado. The experiment was conducted under field conditions during three maize crop succession cycles. The treatments consisted of cultivating maize during the summer, after sorghum and lablab cropped as green manure and fallow during the winter. Higher maize yields were achieved by sorghum–maize succession compared to monocropping, due to higher N fertilizer and biomass inputs to topsoil. Sorghum–maize succession also provided a higher proportion of stable C and N compared to other successions. Maize yields declined as tropical soil fertility intrinsically decreased along three crops succession cycles. Cellulase activity decreased over time, whereas amylase activity increased as the plant residues were already in advanced stages of decomposition. The sorghum–maize crop succession stood out compared to lablab and fallow as it provided the highest maize yields, while maintaining higher C and N levels, and amylase activity. This better performance was likely due to larger amounts of incorporated biomass and better mineral N fertilizer management.

Cover crops in no-tillage systems may alter soil mineral N and influence the N fertilizer use efficiency (NFUE) of subsequent maize. The hypothesis of this work is that no-tillage systems with cover crops affect nitrate, ammonium and maize NFUE in the Brazilian Cerrado. The objective was to evaluate the cover crop mineralization effect on soil N mineral and maize NFUE in a no-tillage system, with and without N topdressing. The experiment was arranged in a randomized block split-plot design. The plots were represented by cover crops (Cajanus cajan, Crotalaria juncea, Raphanus sativus and Mucuna aterrima). The subplots consisted of the application (WN) or non-application (NN) of N topdressing to maize. The soil was sampled in six layers (up to 60 cm) at the end (April) and at the beginning of the rainy season (November). NH4+ was lower for all cover crops and WN and NN management in April. NO3− differed between seasons and cover crops in WN and NN. The lignin concentration and N uptake of M. aterrima were the highest compared to other species. The highest NFUE was on R. sativus, showing higher fertilizer dependency. In a no-tillage system with cover crops, the N topdressing fertilization needs to be improved, considering mineralization.

Edaphoclimatic conditions influence nitrous oxide (N2O) emissions from agricultural systems where soil biochemical properties play a key role. This study addressed cumulative N2O emissions and their relations with soil biochemical properties in a long-term experiment (26 years) with integrated crop–livestock farming systems fertilized with two P and K rates. The farming systems consisted of continuous crops fertilized with half of the recommended P and K rates (CCF1), continuous crops at the recommended P and K rates (CCF2), an integrated crop–livestock system with half of the recommended P and K rates (ICLF1), and an integrated crop–livestock at the recommended P and K rates (ICLF2). The ICLF2 may have promoted the greatest entry of carbon into the soil and positively influenced the soil’s biochemical properties. Total carbon (TC) was highest in ICLF2 in both growing seasons. The particulate and mineral-associated fractions in 2016 and 2017, respectively, and the microbial biomass fraction in the two growing seasons were also very high. Acid phosphatase and arylsulfatase in ICLF1 and ICLF2 were highest in 2016. The soil properties correlated with cumulative N2O emissions were TC, total nitrogen (TN), particulate nitrogen (PN), available nitrogen (AN), mineral-associated organic carbon (MAC), and microbial biomass carbon (MBC). The results indicated that ICLF2 induces an accumulation of more stable organic matter (OM) fractions that are unavailable to the microbiota in the short term and result in lower N2O emissions.

New agricultural practices and land-use intensification in the Cerrado biome have affected the soil carbon stocks. A major part of the native vegetation of the Brazilian Cerrado, a tropical savanna-like ecoregion, has been replaced by crops, which has caused changes in the soil carbon (C) stocks. To ensure the sustainability of this intensified agricultural production, actions have been taken to increase soil C stocks and mitigate greenhouse gas emissions. In the last two decades, new agricultural practices have been adopted in the Cerrado region, and their impact on C stocks needs to be better understood. This subject has been addressed in a systematic review of the existing data in the literature, consisting of 63 articles from the Scopus database. Our review showed that the replacement of Cerrado vegetation by crop species decreased the original soil C stocks (depth 0–30 cm) by 73%, with a peak loss of 61.14 Mg ha−1. However, when analyzing the 0–100 cm layer, 52.4% of the C stock data were higher under cultivated areas than in native Cerrado soils, with a peak gain of 93.6 Mg ha−1. The agricultural practices implemented in the Brazilian Cerrado make low-carbon agriculture in this biome possible.

Resumo:O objetivo deste trabalho foi avaliar a produção de matéria seca e o controle de plantas daninhas por espécies de leguminosas consorciadas com cana-de-açúcar, em cultivo orgânico. As espécies leguminosas Arachis pintoi, Cajanus cajan, Calopogonium mucunoides, Crotalaria anagyroides, Crotalaria juncea e Stylosanthes 'Campo Grande' foram semeadas em novembro de 2012, nas entrelinhas da cana-de-açúcar. O delineamento experimental em blocos ao acaso foi utilizado com quatro repetições e dois controles - um tratamento capinado e outro sem capinar. A massa de matéria seca das leguminosas foi avaliada aos 142 dias após a semeadura (DAS), e a massa de matéria seca de plantas daninhas, aos 29, 85 e 142 DAS. A massa de matéria seca de plantas daninhas foi inferior à da testemunha em todas as épocas amostradas. A produção de massa de matéria seca das leguminosas no consórcio foi baixa. As espécies Crotalaria juncea, Cajanus cajan e Calopogonium mucunoides produziram massa de matéria seca superior à das espécies Arachis pintoi e Stylosanthes 'Campo Grande'. A produtividade de colmos da cana-de-açúcar não foi afetada pelo consórcio. O consórcio entre cana-de-açúcar orgânica e leguminosas com semeadura tardia, para adubação verde, é eficiente no controle de plantas daninhas.

Resumo: O objetivo deste trabalho foi avaliar o efeito do manejo de plantas de cobertura na floração e na maturação fisiológica sobre a produtividade do milho cultivado em sucessão. O experimento, em delineamento de blocos ao acaso com parcelas subdivididas, foi realizado em Latossolo Vermelho, em sistema plantio direto, com nove espécies. Foram avaliados: produtividade de matéria seca; tempo de ciclagem dos resíduos vegetais; teores de N das plantas de cobertura; e produtividade de grãos e teores de N nas folhas do milho. As espécies Pennisetum glaucum, Mucuna aterrima, Cajanus cajan e Canavalia brasiliensis apresentaram as maiores produtividades de matéria seca na floração. Na maturação fisiológica, Sorghum bicolor, P. glaucum, C. brasiliensis, Crotalaria juncea e C. cajan apresentaram produtividades mais elevadas de fitomassa. Não houve efeito da época de corte e da interação planta de cobertura e época de corte sobre a produtividade do milho. As maiores produtividades de milho foram obtidos após cultivo de Urochloa ruziziensis, C. juncea, C. brasiliensis, C. cajan, P. glaucum e Raphanus sativus, e estão relacionadas ao maior acúmulo de matéria seca e ao menor tempo de ciclagem dos resíduos vegetais das plantas de cobertura.